1. Field of the Invention
The invention relates to the field of power semiconductor components.
It proceeds from a turn-off power semiconductor component according to the preamble of the first claim.
2. Discussion of Background
Such a turn-off power semiconductor component is well known and is described, for example, in the article entitled "GTO Thyristors" by Makoto Azuma et al. (Proceedings of the IEEE, Vol. 76, No. 4, April 1988).
Turn-off power semiconductor components of this type are assembled from a multiplicity of standard cells, and have a number of differently doped layers between two main surfaces. Starting from the anode, an n-base and a p-base succeed a, for example p-doped, anode emitter. n-doped cathode emitter regions are recessed into the p-base. Of course, the layers can also be inversely doped. Such components are also known as GTO (Gate Turn-Off Thyristors).
In the case of such gate turn-off thyristors, the penetration depth of the cathode emitter regions in the direction of the anode is selected such that a maximum emitter efficiency results. This is achieved in design terms in present-day GTOs by providing that the cathode emitter has an edge concentration of 10.sup.20 cm.sup.-3 and a depth of the pn junction of approximately 10 .mu.m. The result is that the fraction of the minority carrier current in the emitter is normally below 1%. Because of the high emitter efficiency, the space below the emitter is filled with a very high plasma density, and this ensures the required, low conducting-state power losses. However, the high plasma density tends to instability, in particular in the case of turn-off. The consequences for present-day GTOs are known: limited turn-off capacity and current filamentation. In order to limit the influence of these disadvantages, lifetime-reducing measures such as irradiation and the production of recombination centers are undertaken in the GTO. Furthermore, the anodes of the GTOs are provided with strong anode short circuits for extracting the plasma as quickly as possible during turn off. However, like the production of recombination centers, as well, this measure substantially worsens the conduction of the component. The present-day dimensioning philosophy is therefore self-contradictory.
Already today, but to an even greater extent in future applications, high demands are placed on the current and voltage loadability of the power semiconductor components. Here, the abovementioned disadvantages set limits to the present-day, known GTOs, because they can be destroyed, in particular by excessively high local loads, due to current filamentation. In order to prevent this destruction, the present day GTOs must be operated with an extensive protecting circuit.